How to configure StreamArn of existing dynamodb table

Question

I'm creating serverless framework project.

DynamoDB table is created by other CloudFormation Stack.

How I can refer existing dynamodb table's StreamArn in serverless.yml

I have configuration as below

resources:
  Resources:
    MyDbTable: //'arn:aws:dynamodb:us-east-2:xxxx:table/MyTable'
provider:
  name: aws
  ...
  onDBUpdate:
    handler: handler.onDBUpdate
    events:
      - stream:
        type: dynamodb
        arn:
          Fn::GetAtt:
            - MyDbTable
            - StreamArn

Answer 1

EDIT:
- If your tables were created in another Serverless service you can skip steps 1, 4 and 8.
- If your tables were created in a standard CloudFormation Stack, edit this stack to add the outputs from step 2 and skip steps 1, 4 and 8

---

Stuck with the same issue I came up the following workaround:

1. Create a new serverless service with only tables in it (you want to make a copy of your existing tables set-up):

       service: MyResourcesStack
   
       resources:
         Resources:
         FoosTable:
           Type: AWS::DynamoDB::Table
           Properties:
             TableName: ${opt:stage}-${self:service}-foos
             AttributeDefinitions:
               - AttributeName: id
                 AttributeType: S
             KeySchema:
               - AttributeName: id
                 KeyType: HASH
             ProvisionedThroughput:
               ReadCapacityUnits: 1
               WriteCapacityUnits: 1
             StreamSpecification:
               StreamViewType: NEW_AND_OLD_IMAGES # This enables the table's stream
   

   (Optional) You can use serverless-dynamodb-autoscaling to configure autoscaling from the serverless.yml:

   plugins:
     - serverless-dynamodb-autoscaling
   
   custom:
     capacities:
       - table: FoosTable  # DynamoDB Resource
         read:
           minimum: 5        # Minimum read capacity
           maximum: 50     # Maximum read capacity
           usage: 0.75       # Targeted usage percentage
         write:
           minimum: 5      # Minimum write capacity
           maximum: 50      # Maximum write capacity
           usage: 0.75       # Targeted usage percentage
   

2. Set up the stack to output the tables name, Arn and StreamArn:

       Outputs:
         FoosTableName:
           Value:
             Ref: FoosTable
         FoosTableArn:
           Value: {"Fn::GetAtt": ["FoosTable", "Arn"]}
         FoosTableStreamArn:
           Value: {"Fn::GetAtt": ["FoosTable", "StreamArn"]}
   

3. Deploy the stack

4. Copy the data from your old tables to the newly created ones.
   To do so, I used this script which works well if the old and new tables are in the same region and if the table are not huge. For larger tables, you may want to use AWS Data Pipeline.

5. Replace your hardcoded references to your tables in your initial service with the previously outputed variables:

       provider:
         environment:
           stage: ${opt:stage}
           region: ${self:provider.region}
           dynamoDBTablesStack: "MyResourcesStack-${opt:stage}" # Your resources stack's name and the current stage
           foosTable: "${cf:${self:provider.environment.dynamoDBTablesStack}.FoosTableName}"
           foosTableArn: "${cf:${self:provider.environment.dynamoDBTablesStack}.FoosTableArn}"
           foosTableStreamArn: "${cf:${self:provider.environment.dynamoDBTablesStack}.FoosTableStreamArn}"
   
       functions:
         myFunction:
           handler: myFunction.handler
           events:
             - stream:
                 batchSize: 100
                 type: dynamodb
                 arn: ${self:provider.environment.foosStreamArn}
   

6. Deploy those changes

7. Test everything
8. Backup and delete your old tables